Synthetic wood pulp has long been recognized in the prior art as being particularly useful for the production of paper-like substrates. Such pulp, which ordinarily consists essentially of fibrils or short lengths of polymeric fibers, has long been known to be useful as a replacement for wood pulp and, in particular, to be susceptible to formation into synthetic wood products in essentially the same manner as has been utilized for natural wood pulp.
The production of these fibrils has normally been performed through steps comprising refining solid polyolefinic fiber in organic dispersant under conditions of high shear stress followed by the replacement of the original dispersant--either directly or by means of one or more intermediate liquid media--with water so as to form an essentially aqueous slurry of the polyolefin.
The prior art is replete with techniques for the initial production of suitable polymeric fibers. Ordinarily, such fibers are formed in a liquid hydrocarbon by techniques, the most notable of which are fiber spinning, shear precipitation and thermal precipitation. Representative of these suitable hydrocarbons are: aromatics--such as benzene, toluene; aliphatics--such as butane, hexane, octane; alicyclics--such as cyclohexane; and halogenated aliphatics--such as methylchloride, carbontetrachloride.
By way of example, fibers have been formed by ejecting hydrocarbon solution of polyolefin through spinnerets to form continuous filaments as in U.S. Pat. No. 3,081,519, while in U.S. Pat. No. 3,743,272 there is disclosed a process whereby high molecular weight polyolefin may both be produced in a hydrocarbon and formed into fibers upon subsequent precipitation of the polymer therefrom by cooling.
The particular means by which the initial polymer fibers are formed is not, however, critical. What is important is that in essentially all the prior art processes, solid polyolefinic fibers having molecular weights in excess of 200,000 and ordinarily in excess of 500,000 are produced in a hydrocarbon vehicle. The conversion of these fibers to useful form may be accomplished by subjecting a slurry of the fibers to high shear stress. The minimum shear stress required for the formation of such structures depends somewhat upon the particular polymer and medium utilized. It is well known within the ordinary skill in the art, however, to determine the necessary conditions of, for example, agitator velocity and angle of incidence which are necessary for the production of a pulp useful, inter alia, for the production of paper and paper-like structures.
Numerous refining media for dispersing the fibers are also known in the prior art. One such technique simply utilizes the liquid hydrocarbon in which the fibers are originally formed. More commonly, however, it is desired first to transfer such fibers to a second medium for fibrid production. Accordingly, the initial hydrocarbon dispersant is ordinarily replaced with an organic solvent miscible therewith so as both to facilitate the transfer and simultaneously to purify the fibers of such hydrocarbon which generally exhibits disagreeable properties.
After formation of useful fiber pulp--either in the initial hydrocarbon solvent or in one of the usual replacement media therefor--it is desirable to convert it to an essentially aqueous slurry. Accordingly, the refining medium which disperses refined polymer may be replaced with water to facilitate production of paper and paper-like films in the same manner, and on the conventional equipment, utilized in the production of paper from aqueous wood pulp slurries.